Apparatus for heating the air blast for furnaces and the like



, March 18, 1930. I DOVEL 1,751,136

APPARATUS FOR HEATING THE AIR BLAST FOR FURNACES AND THE LIKE Filed Dec.16. 1926 3 Sheets-Sheet l 5 A 7g 1 I 5.-

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' rwentcl James P, Dovel Gnome March 18,1930.

J.' P. D OVEL Filed Dec. 16,1926

APPARATUS FOR HEATING THE AIR BLAST FOR FURNACES AND THE LIKE sShets-Sheet 2 @uomu J. P. DOVEL 1,751,136

APPARATUS FOR HEATING THE AIR BLAST FOR FURNACES AND THE LIKE March 18,1930.

Filed Dec. 16, 1926 3 Sheets-Sheet esRDozfel Gnome Patented Mar. 18;1930 UNITED STATES PATENT OFFICE,

JAMES P. DOVEL, or BIRMINGHAM, ALABAMA Application med December 1a,1926. Serial No. 155,277.

My invention relates to a new and improved process for the heating ofthe air blasts delivered to blast furnaces, cupolas, or

wherever it is desired to heat the air blast,-

5 and to an apparatus for carryingmy said a process into effect.

While it is to be understood that my invention is applicable forservicein heating any type of blast I shall hereinafter describe it morepartlcularly with reference to its. application to blast furnaces, butwithout thereby intending to limit myself to such specific use. i

- In Letters Patent No. 1,316,086, issued to me on September 16th, 1919,I have shown and described an air heater connected in a p by-pass acrossthe cold air main and through this heater the waste gases from thestoves are passed in their flow to the stack. By con- 26 trolling thevolume of cold air delivered to the heat transfer apparatus it waspossible to absorb from the waste gases all heat in excess of thatrequired to maintain the necessary draft in the stack.

In the practical applicationof this process I'have discovered that amore efficient and a materially less expensive means for heating theblast can behad by the simple enlargement or increase in capacity'of myair heater 30 andby supplementing the heat supplied thereto by the wastegases with burning gas or a like source of heat of active combustloncontrollable in amount and regulable so that the aggregate of heat '1[nits delivered from the waste gases and the burning gases will enablethe heater to preheat the cold'air blast to the desired temperaturewithout robbing the stack of its necessary heat, unless the draft Ithe-rein be maintained by a blower or'fan.

Another distinctive feature of my present process is the blending of thelow and high temperature gases prior to their delivery to the transferelements in the air heater, there- 'by to reduce the temperature of thegases entering the heater sufficiently to, avoid injury to the'heattransfer elements. lthas been demonstrated that the transfer of heatdithrough the transfer elements of my present type of heater to the airblast is a 0 more efiicient means of heating same than -drawings, inwhich I have illustrated the preby the indirect methods of the stoves.and in practical experience I have demonstrated that" my improved airheater for the cold bl'as't,- representing an initial installation costof less than half that of stoves and with prac- 56 tically negli iblemaintenance cost, has enabled me to dispense with one stove and still tomaintain a suitable temperature in the hot blast with a marked economyin consumption. The desirability of blending the high and mediumtemperature (gases delivered to the air heater arises from the factthatfrom the point of view of prime cost it is desirable to make the heaterof standard cast iron pipe which can be obtained at low cost and can beassembled with the available help at the furnace and maintained with butslight expense. Such heat transfer elements would not stand the hightemperaturesof direct combustion, and to this end my present inventioncontemplates blending the flame of the burning gases I with the wastegases from the stoves in a Dutch oven or equivalent apparatus connectedwiththe air heater and provided with suitable refractory elementstherein to insure an equalization of the different temperatures thereinof the gases delivered to the heater. The refractory elements in theDutch ovenare of negligible cost and of easy replacement and thus do notrepresent, to any appreciable extent, an element of cost in theoperation of the process.

The practice of my process will be better understood by reference to theaccompanying ferred type of mechanism for carrying same into efiect.

Fig. 1 is a view in side elevation of a conventional arrangementofstoves for a blast furnace with the stack flue 'and airheater 7 shown invertical cross-section.

Fig. 2 is a transverse detail sectional view of the Dutch oven and theadjacent end of the heater taken along the line l L-ell t of Fig. 3;

r Fig. 3 is a vertical longitudinal cross-section of theapparatus; and

ratua Fig, 41s a sectional plan view of the appa- Similar referencenumerals refer to simi 1211' parts through out the drawings. In theapparatus illustrated, 1 is the hot main from the stoves 2 to the blastfurnace V7 or other source of use (not shown), and 3 is disposed top andbottom bafiies l0 and 11 to cause a tortuous flow of the gases therevthrough until dischar edthrough a flue 12 to the stack or otherischarge'. Thev Dutch oven and the air heater maybe built up in 9accordance with any standard practice and therefore need not bespecifically described otherwise than'to state that the cdnstru'cti'onis such as to withstand stovetemperatures. The cold blast main 13 leadsabove the air heater and is provided with by-pass connections 14 and 15totheend's of the air heater.

I interpose a by-pass valve 16 beyond the connection 14 in the coldblast main, and also a valve 17 for the by-pass'connection 14, and asimilar valve 18 in the connection 15. The valve 16 is of any suitablety e which is adapted to be opened and closed y means of a bell crank 19pivotally mounted on a stand ard 20 on the main 13 and having itsvertically disposed arm connected to a thermostatic bar 21 which rojectsinto. the stack and is slidable throng 'a stulfing-box 22 suit-.

, ably anchored in the stack.- The bell crank is given an adjustableconnection to the valve stem, as described in my Letters "Patentaforesaid, to which reference is made for a more detailed description ofthe automatic thermostatic control of thevolume of cold-airbypassedthrough'the air heater. The cold air entering the air heater by means ofthe connection 14 is delivered to a header 23 having a transverse seriesof elbow fittings 24 connected thereto and downturned to receive pipecoils 25 which form the heat transfer 5 elements. 'These coils extend'bontinuously the full length of the air heater and comprise vertical"legs connected topandflbottom by U-bends'26, the lower U-bends beingseated on. low cradles 27 on the floor of the air heater and theU-ben'ds are provided over head with. erforated lugs 28 which receive vconnectin are 29 having spacer sleeves30 interpose so that the. heattransfer elements are suitably connected and spaced overhead so as toprevent vibration. Each heating coil at its end delivers the heated airthrou h an end elbow 24 to a header '31 from whic the connection 15leads back-tothe cold main.

1 Live gas through a main-"32 and connection 33 is delivered to a header34 under-.-

:control of the valve 35, and from the header 34 lead suitable burners36 which deliver through the outer end wall of the Dutch oven.- Iinterpose suitable refractory material 37, preferably in checker-Workdesign in this Dutch oven and I interpose samebetween the burner nozzles36 and the ports 8 so that the flame from the burning gases,

delivered from the burners 36, will impinge against this refractory massand be broken 'up and diverted in all directions to'the-end that it willbecome properly and uniformly mixed with the waste gases entering throuh the connection 6, thus causing the gases elivered through ports 8 toenter the air heater at a safe temperature for the durable serv ice ofthe heat'transfer elements therein. As

illustrative of what I have in mind, when gases passing into theairheater will be about 1400 E, which is a safe temperature for the typeof heat transfer elements used. Obviously if better heat resistanttransfer ele-- ments were used in the "air heater higher entering gastemperatures could be used therein and thus, a greater percentage ofburning gases used. i A

The air heater is provided at suitable intervals, preferably adjacent toitsbaflles, with transverse bottom openings 38 which extend to each sideof the airheater and are there provided with removable gratings 39 bywhich access may be had for clean out pur-" poses. The cradles 27falling opposite these openings are supported on cross beams 40 and theends of the headers 23 and-31,.which project through the casing, aresupported by cross members 41 of its metallic frama The clean out spaceunder the gratings 39 1s norby manhole doors 42. It' is of advantage tonote that heat transfer coilswhile-suitably supported and bracedtogether, are 'all'free to expand and contract in the air heater and arereadily accessible for replacement and repair at any point. 7 In orderto keep these In operation, with the apparatus set up -mally shut offfrom the bottom openings-38 and connected substantially in the 'manner 1above described, the thermostatic valve 16 will control the volume ofcold air byassed from the cold air main through the air eater,maintaining this volume as large as will=leave the desired amount ofheat in the exhaust gases in the stack or like point of discharge,

and thus recoverable heat from the waste gases of the stoves istransferred to the cold blast. In order to raise this cold blast to asufficiently high temperature to enable a part of the stove ca acity forthe furnace to be dispensed with, deliver through the burners in theDutch oven suflicient live gas, which burning in the oven and minglingwith the entering waste gases will raise the tempera-,

ture of such gases as high as may be desired within the limitscontemplated for the heat transfer elements of the air heater. Toillustrate, if sufiicientlive gas is burned to raise the temperature ofthe waste gases entering the'air heater to 1400 F., I have found itpossible to raise the temperature of the air blast sufficiently toreduce the duty on the stoves enough to enable a part of'them to bediscontinued and I accomplish this highly desirable end with an outlayas to cost much less than that of the discontinued stove ca pacity.Moreover,-I obtain a much more efli- I cient and more uniform and moreaccurately cont-rolled transfer of heat to the. air blast than where theindirect methods of transferring heat, as by stoves, is employed, and Iam able to bring the heat transfer apparatus up to full service veryrapidly, which is obviously impossible with stoves. The pro vision ofthe refractory mass in the Dutch oven is optional, as any arrangement ofde sign may be provided which will effect a mingling of the gasesentering the Dutch oven an an avera 'ng of their temperatures beforethey enter t e air heater.

The feature to which my present invention is broadly directed, consistsin a combined heat recuperating means having a combus tion chamberrovided with means to produce therein igh temperatures by active gaseswith the, high temperature gases of active combustion andpass thecommingled gases through said combustion chamber and ments in saidcombustion chamber interposed in the path of the waste gases and thegases of active combustion to more effectively mix the same before theyass into the. heat recuperating means, an' means to pass air combustion,means to commingle said waste 1 heat recuperating means, refractoryelethrough said heat recuperating means into said cold air main.

In testimony whereof I aflix my si JAMES 1?. DO L.

ature.

live and waste heat means controllable so as I to deliver to a heattransfer for the cold blast the requisite volume of blended hot gases topreheat the cold blast to the stoves to the desired extent without atthe same time interferin with the necessary draft, for conducting t efurnace gases through the stoves and heat transfer to the desired ointof utilization or discharge, and wit out subjecting,

the heat transfer to excessive temperatures. Though I have described myinvention more particularly as applied to blast furnaces where such termis used, it is inclusive 1 of any type of furnace or heating unitwherein waste gases are present andthe preheating of air delivered tothe furnace or heater would be desirable.

Though I have described with great particularity the details of theembodimentof the invention herein shown, it'is not to be construed thatI am limited thereto, as changes in arran ement and substitution ofequivalents may e made by those skilled in the art without departin fromthe invention as defined in the appen ed claim.

Having thus described my invention, what

